Functionalization and cleavage of coordinated dinitrogen via hydroboration using primary and secondary boranes

The reaction of the side-on, end-on ditantalum dinitrogen complex ([NPN]Ta) 2 (µ-η 1 :η 2 -N 2 )(µ-H) 2 (where NPN = PhP(CH 2 SiMe 2 NPh) 2 ) with a variety of secondary and primary boranes is reported. With 9-BBN, hydroboration of the Ta 2 N 2 unit occurs via B-H addition, which in turn triggers a cascade of reactions that result in N—N bond cleavage, ancillary ligand rearrangement involving silicon group migration, and finally elimination of benzene from the N-Ph group and a B-H moiety to generate the imide–nitride derivative. In the presence of excess 9-BBN, the Lewis acid – base adduct of the imide–nitride ([NPµ–N]Ta(=NBC 8 H 14 )(µ-NB(H)C 8 H 14 )Ta[NPN]) is formed. A similar set of reactions is observed for dicyclohexylborane (Cy 2 BH), which hydroborates the dinitrogen complex to generate [NPN]Ta(H)(µ-η 1 :η 2 -NNBCy 2 )(µ-H) 2 Ta[NPN], followed by loss of H 2 and silicon group migration to yield the imide–nitride [NPµ–N]Ta(=NBCy 2 )(µ-N)(Ta[NPN]. With thexyl borane (H 2 BCMe 2 CHMe 2 ), a similar sequence of reactions is suggested starting with hydroboration to generate [NPN]Ta(H)(µ-η 1 :η 2 -NNB(H)C 6 H 13 )(µ-H) 2 Ta[NPN], followed by loss of H 2 and ancillary ligand rearrangement. When bis(pentafluorophenyl)borane (HB(C 6 F 5 ) 2 ) is used, no hydroboration of coordinated N 2 is observed, rather simple adduct formation to give ([NPN]Ta) 2 (µ-η 1 :η 2 -NN-B(H)(C 6 F 5 ) 2 )(µ-H) 2 occurs.